Airbags have proved effective in protecting occupants of motor vehicles during accidents. New vehicles usually offer airbags for the driver's side, and sometimes passenger's side, of the vehicle front seat. Such airbags are installed within the vehicle steering wheel or dashboard. The airbag is usually activated by sensors positioned under the vehicle hood near the front of the vehicle. A predetermined impact activates the sensors, which communicate with a computer to direct the airbag inflation. Commonly, the ignition of a small amount of volatile chemical (such as sodium azide) produces gaseous nitrogen to inflate the airbag within about 0.05 seconds after an impact. Such airbags are typically made of opaque, carbon-reinforced plastic and deflate within a few hundredths of a second after inflation.
While such airbag systems usually provide excellent protection, disadvantages exist. The complicated electronics associated with airbags are vulnerable to malfunction, especially if exposed to heat, vibration, and corrosive elements under the hood of the vehicle.
For cars not factory equipped with airbags, retrofit airbag systems have been developed. However, the activation systems of these retrofittable airbag systems are generally less than satisfactory. U.S. Pat. No. 5,322,326 to Ohm shows a retrofittable airbag system with a complicated mechanical linkage that inflates the airbag by piercing a compressed gas canister seal during an accident. In addition to being expensive to produce, the series of moving parts in the mechanical linkage may yield unreliable and somewhat delayed airbag inflation. The piercing of the gas canister during system activation also delays airbag inflation. As a result of the delayed airbag inflation, only relatively small airbags offering limited protection may be practical with such a activation system.
Other retrofittable airbags are also less than satisfactory in that they may rely on malfunction-prone electronic or magnetic systems for airbag inflation. Such retrofit inflation systems also tend to activate relatively slowly, and inflate relatively small airbags that provide limited protection.